Anemia is the condition of having a low count of red blood cells. These are the cells in the body that carry and distribute oxygen. Macrocytic refers to the enlarged size of the red blood cells. The most common causes of macrocytic anemia are vitamin deficiencies, alcohol use, certain medications and thyroid disorders.
Vitamin B12 Deficiency
This is usually caused by a problem absorbing the vitamin from the gut. It can also develop in people who are on very limited diets or who have had surgery for weight loss.
Folate Deficiency
Folate is another B vitamin. A deficiency may occur through inadequate dietary intake, or through a problem with absorption of folate. Some medications, such as anti-inflammatories and birth control pills, can impair its absorption.
Medications
Many medicines can cause a macrocytic anemia either by impairing B12 and folate metabolism or by other mechanisms. Some drugs used to treat HIV infection, some anti-seizure medicines and some antibiotics can be implicated. Other specific drugs like metformin, methotrexate, and cholestyramine are common offenders.
Alcohol Abuse
Alcohol can cause a macrocytic anemia through direct toxic effects. In addition, many alcoholics have poor nutritional habits and have a low intake of folate and/or vitamin B12.
Bone Marrow Disorders
Because red blood cells are produced in the bone marrow, problems here can lead to a macrocytic anemia. This would include some types of leukemia or lymphoma.
Liver Disease
The liver is involved in production and metabolism of red blood cells, so various disorders of the organ can cause anemia. Things like hepatitis or liver cancer could be involved. Alcohol use may lead to macrocytic anemia by damaging the liver as well.
Blood Loss
Following blood loss or during ongoing blood loss, the production of red blood cells increases. Newly produced red blood cells are larger than mature forms. The anemia from blood loss may be classified as macrocytic due to these larger, immature cells.
Lung Disease
Chronic obstructive pulmonary disease or emphysema can lead to anemia. The mechanism for the macrocytosis is increased red blood cell production to make up for the lack of oxygen coming into the body. Production is increased in order to raise the ability of the blood to carry the oxygen that is present.
Hypothyroidism
An underactive thyroid gland can lead to macrocytic anemia.
Splenectomy
Surgical removal of the spleen leads to an increased risk of macrocytic anemia due to the spleen's role in processing red blood cells.
Nitrous Oxide
Abuse of "laughing gas" is an uncommon cause of macrocytic anemia. It affects vitamin B12 metabolism and decreases oxygen in the bloodstream.
